Mare Seasonality

The mare is a seasonal breeder with a series of estrous cycle normally occurring the breeding season which coincides with long day lengths. The longest day of the year is June 22 and the shortest is December 22. Therefore mares should reach a peak in their reproductive activity around June 22 and be the least reproductively active in late December.

Anestrous period

The period in which the mare is the least reproductively active is termed the “anestrus” period and typically …

Pasture Breeding Horses


While total conception rates are no less with pasture breeding, most mare owners require specific breeding dates so that expected foaling dates can be accurately calculated. Some breed registries, most notably The Jockey Club, require natural cover. In addition to requirements imposed by registries, some managers prefer natural service because of lower investments in labor and equipment. Conversely, natural matings can be more dangerous because of the differences in mares’ acceptance to a stallion and the stallion’s conduct around them. …

Evaluation of Stallion Semen

Evaluating Semen Quality 


Keep all equipment used in semen evaluation at 37°C and free of any spermicidal agents. Evaluate each ejaculate to assure the maximum number of normal, progressively motile spermatozoa. The following criteria are used to determine semen quality, total sperm output and insemination dose: volume, concentration, motility and morphology.


Volume is simply the total amount of gel-free semen in a single ejaculate and is usually measured in milliliters.


Concentration is determined by using a hemocytometer or …

Processed Stallion Semen

As reproductive technologies increase, the use of cooled or processed stallion semen is becoming more prominent. However use of processed semen requires certain management procedures. This article discusses the process of using cooled stallion semen, the potential problems, and certain breed restrictions.
Using cooled semen in a breeding program is becoming a much more viable option for many horse producers. It does involve more coordination and organization between mare owner, stallion manager and veterinarian. However, it is a fairly simple

Foal Heat Mares

Postpartum mares will have a “foal heat” 7 to 14 days following foaling, and a second cycle approximately 30 days later.

Breeding on foal heat is still somewhat of a controversial practice. Mares are usually bred on foal heat as long as three criteria are met.

  1. The mare has a normal foaling, that is she does not have excessive bruising or tearing.
  2. The mare does not retain the placenta for more three hours.
  3. Upon palpation and ultrasound exam the uterus

Stallion Anatomy Exam

External Reproductive Organs

Penis and Prepuce 

The stallion’s penis consists of 3 parts: (1) the root or bulb, (2) the body or shaft, (the main part), and (3) the glans, the enlarged free end of the penis. When not erect, the penis is 50 cm long and 2.5 to 6 cm in diameter with the distal end 15 to 20 cm free in the prepuce. When erect, the penis doubles in length and thickness and the glans increases by 3 …

Twinning in Mares

Twinning in mares is very undesirable because of low survival rates, usually very weak foals, and numerous conformational problems. Of all twin pregnancies, 60% will birth a live single foal, 31% will abort both foals, and 9% will carry both twins to term. Of the 9% carried to term, 64.5% will birth two stillborn foals, 21% will birth one live foal and one stillborn foal and 14.5% will birth two live foals.

Mare with Twins


Two separate ovulations occurring a day apart …

Understanding Horse Reproduction

Many producers who raise horses find breeding horses rewarding, yet frustrating. Mares and stallions are traditionally placed in the breeding herd due to successful performance records, with little consideration for their reproductive capabilities. Horses are difficult breeders with an estimated foaling rate of below 60 percent. Various factors contribute to this and basic understanding of equine reproductive physiology can improve reproductive efficiency and foaling rates. The breeding manager’s goal should be to get the maximum number of mares pregnant, in …

Horse Semen Collection

Semen Collection 

Stallion Collection

Collection with a breeding phantom

In collecting semen from a stallion, a jump mare or breeding phantom is commonly used. Stallions can be easily trained to mount a breeding phantom. Those trained to mount a phantom make collection much safer and more consistent. The phantom should be designed to be comfortable for the stallion and should mimic the same angle as the mare. If a jump mare is used, she should be in good standing heat and have …

Management of the Pregnant Mare

Gestation Length

The average gestation length (duration of pregnancy) of mares is 335 to 340 days, but can range from 320 to 370 days. There may be much variability among mares, but most individually follow similar patterns year after year. Foals are considered premature if delivered at less than 326 days of gestation and usually require immediate veterinary attention. Mares foaling before 310 days are considered to have aborted. Many breeders will calculate the expected foaling date at 11 months …